While I was out installing the new backup camera, I started hearing a static on two of the Radio speakers. It was one on each side, the second ones back from the front. The radio was turned off, the ignition was off.
A buildup of static electricity can cause speakers to sound off. Did the static just last a very short time and then stop or did it continue? If it was a one time short duration, static electricity could be the answer. If not, you may have electrical wiring running parallel and adjacent to your speaker wires that is causing electro-magnetic interference. Another thought, some radios are wired in such a way that they are never completely off unless the battery is disconnected. This allows the clock to remain running. If an internal short is developing in the radio, that could also result in crackling of the speakers when the unit is theoretically off.
__________________
Michael and Georgia Day
1992 Newell 43.5' #281
8V92 DDEC-2, HT740
PT Cruiser GT with Remco Transmission Pump https://newellowner.com/newell-photos/